Light emitting diodes (“LEDs”) are, in general, miniature semiconductors that employ a form of electroluminescence resulting from the electronic excitation of a semiconductor material, which produces visible light. Initially, the use of LEDs was limited mainly to display functions on electronic appliances and the colors emitted were red and green. As the technology has improved, LEDs have become more powerful and available in a wide spectrum of colors.
As LEDs have become more powerful, they have also become smaller, brighter, more efficient and less expensive. LEDs are now found in an ever increasing number of applications. With the increasing capabilities of LEDs, a possibility now exists for using LEDs for illumination in generally conventional lighting applications. The advantages of using LEDs for illumination is that they are far more efficient than conventional lighting, are rugged and very compact, and can last much longer than incandescent or fluorescent light bulbs or lamps. However, one disadvantage of using LED devices in general conventional lighting application is that LED devices are generally directional light emitters.
FIG. 1 illustrates the cross-sectional structure of a typical LED device 100. The LED device 100 is provided with a mount lead 102 and an inner lead 104. The mount lead 102 also includes a reflector cup 106 or an opaque substrate, in which a light emitting diode or LED chip 108 is affixed. An n electrode and a p electrode of the light emitting diode 108 are connected to the mount lead 102 and the inner lead 104 by bonding wires 110 and 112, respectively. The whole assembly is encapsulated in a clear encapsulate 114. In operation, the LED 102 emits directional light upward 116, toward the top of the LED device 100.
In practice, most light 116 in LED devices 100 are emitted from the top surface and the four side surfaces of the LED chip 108. Almost no light is emitted from the bottom surface of the LED chip 108 after it is packaged into an LED device 100, as shown in FIG. 1. This is because the reflector cup 106 or opaque substrate located on the mount lead 102 of the LED device 100 blocks all the light on the bottom surface of the LED 108 and generally reflects the light 116 from the four sides of the LED chip 108 upward. Accordingly, in prior art LED devices 100, light 116 is emitted only in the forward hemisphere of the LED device 100. In that respect, a LED device 100 is considered a directional emitter, having a beam pattern typically of 120 degrees or less.
In other prior art LED devices, the LED chip is assembled inside a reflector-like cavity that serves to collect all the four side lights and reflect them towards the top direction, thus making the LED device even more directional. The beam pattern of this type of LED device is typically not more than 60 degrees.
While LEDs offer many advances over conventional lighting, many generally lighting applications utilize omni-directional light sources, i.e., a light source capable of emitting light in all directions (360 degrees). Since typical LED devices only emit light in one direction, the use of LED devices for illumination in general lighting applications is limited. A need therefore exists for a LED device designed to allow the light from an LED to be emitted omni-directionally, thereby increasing the application of LEDs in general lighting applications or other application in which omni-directional lighting is desired or useful.